Description

The specimen from deeper water was nearly round, except for the slightly auriculated cardinal margin; the teeth were also proportionally more distant and less strong, the exterior nearly smooth. I suspect it to be different, but until further material be available, refer it to this species as a variety orbiculata. I can only account for Prof. Verrill's suggestion that this species and Arca glacialis are the same, and that Sars' figure of the variety septentrionalis represent a deformed specimen,* by the supposition that the Professor had no specimens of the genuine A. glacialis for reference. It appears to me not only that they are very distinct, but that many authors would be tempted to put them in different sections of the genus. Apropos of this, the reference of these small species to Cucullæa by Dr. Jeffreys will hardly be accepted in view of the char­acters of the type of Lamarck's genus, which materially differ from those of the forms now under consideration. In this species sometimes the radiating sculp­ture almost fails, at other times is very strong; the margin is sometimes lightly notched on the edge, but is smooth within the edge; in the middle of the hinge margin is an edentulous space, and all the teeth are more or less oblique.”